interviews with suspects in ways that do not effectively encourage
the suspects to speak (see chapter 4), they will produce fewer
speech cues. This is one reason why police interviewers who are
unprepared and not properly trained may often make lie detec-
tion mistakes when interviewing suspects (e.g. letting a guilty
person go free).
So how might professionals become better lie detectors? First of
all, they need proper training on how to conduct information gath-
ering investigative interviews (see chapter 4). Secondly, they need
training (based on the results of relevant, published, quality
research rather than on speculation) to avoid relying on the stereo-
typical but wrong cues (see above), and guidance on which cues
can be better guides, with the clear acknowledgement that even
these cues are not that reliable as indications of lying. Furthermore,
they need training to overcome other false beliefs such as (i) honest
or attractive-looking people lie less and (ii) people who look
nervous are liars (when they are probably just socially anxious or
introverted). Then, they need to understand that if professionals
behave in an accusatory or aggressive or suspicious way this in itself
may well result in the person giving off cues that the professionals
believe to be signs of lying. They also need training to combine
useful cues from behaviour and from speech (see the section below
on combining lie detection methods). Finally, they need guidance
on how to avoid revealing near the beginning of the interview most
or all of the information they have about the crime and the suspect
(see chapter 4).
training to detect deception from behaviour
A number of books that claim to improve people’s ability to detect
deception have been published. However, many of the behaviours
these books claim to be guides to deception are not valid cues. A
small number of better quality research studies have been pub-
lished in which participants observe video recordings of people
that have been analysed for which behaviours best discriminated
between their lying and truth-telling. Some of the participants
were told which cues actually discriminated and some were not.
72 criminal psychology: a beginner’s guide